A popular method for measuring the concentration of a particular component contained in a sample liquid (e.g. glucose in blood) utilizes oxidation-reduction reaction. Portable hand-held blood glucose level measuring apparatuses are available so that the user can easily check the blood glucose level while staying at home or away from home. To measure the blood glucose level using such a portable blood glucose level measuring apparatus, a disposable biosensor for providing an enzyme reaction system is attached to the measuring apparatus, and then blood is supplied to biosensor for the measurement of the blood glucose level (See JP-B-8-10208, for example).
Various types of biosensors have been put to practical use, an example of which is shown in FIGS. 11 and 12 of the accompanying drawings. The illustrated biosensor 9 includes a substrate 92, a spacer 93, a cover 94, and a capillary 95 defined by these parts. The substrate 92 is formed with an operative electrode 90 and a counterpart electrode 91. A portion 90a of the operative electrode 90 and a portion 91a of the counterpart electrode 91 are located within the capillary 95 and connected to each other by a reagent portion 96. The reagent portion 96 contains oxidoreductase and an electron carrier. The cover 94 is formed with a discharge port 94a and laminated on the substrate 92 via the spacer 93. The interior of the capillary 95 communicates with the outside through an open end 93a of a slit 93A and the discharge port 94a. 
For measuring the blood glucose level, blood is introduced to the capillary 95 of the biosensor 9, which is pre-mounted to the blood glucose level measuring apparatus. The blood moves through the capillary 95 to the discharge port 94a by capillary action while dissolving the reagent portion 96 to form a liquid phase reaction system in the capillary 95. The concentration measuring apparatus determines whether or not the sample liquid introduced into the capillary 95 based on to the response current (or the voltage converted from the response current) obtained by utilizing the operative electrode 90 and the counterpart electrode 91. Specifically, when the response current (or the responsive voltage) is equal to or higher than a predetermined threshold value, it is determined that the blood is supplied.
In the liquid phase reaction system in the capillary 95, the glucose in the blood is oxidized while the electron carrier is reduced by the catalytic reaction of oxidoreductase. When certain voltage is applied to the liquid phase reaction system, the electron carrier is oxidized (releases electrons), and the electrons released by the electron carrier is supplied to the operative electrode 90. The blood glucose level measuring apparatus measures the supply of electrons to the operative electrode 90 as the oxidation current, and computes the glucose level based on the oxidation current.
The response current reflects the supply of electrons to the operative electrode 90, and the electron supply to the operative electrode 90 reflects the amount of oxidized glucose, i.e. the glucose level. However, the blood contains blood cell components such as red blood cells, and the response current varies depending on the amount of the blood cell components. The amount of blood cell components in blood (hematocrit) differs among individuals and varies depending on physical condition even in the same person. Therefore, due to the influence of hematocrit, proper measurement may be impossible even when the same person performs measurement, let alone when the users are different. Further, the response current measured may be influenced not only by hematocrit but also by the degree of chyle or hemolysis of blood, for example.
The influence of hematocrit may be eliminated by a method in which the hematocrit of the blood is measured in advance and the blood glucose level is calculated while taking the hematocrit into consideration (See JP-A-11-194108, for example).
However, the concentration measurement by such a method is troublesome, because the hematocrit need be inputted in the blood glucose level measuring apparatus. The operation for inputting hematocrit is particularly troublesome in a medical facility, for example, in which a single blood glucose level measuring apparatus need be used frequently for measuring the blood glucose level of a large number of patients. Moreover, before the use of the blood glucose level measuring apparatus, another apparatus need be used for measuring the hematocrit of the patient, which makes the method further troublesome.